DIY paint job using SPRAY PAINT, few questions

[bufmatmuslepants]

over the past few weeks ive been wet sanding and prepping my truck for a cheapo paint job and i have a few questions as i get closer to time to paint. ive been using an abrasive pad from advanceauto on a semislow speed drill to take off the surface rust and peeling paint, and a rubber sanding block with 320 grit to wetsand, using a carwash sponge to apply the water keeping the surface wet. duplicolor rattle can high-build primer is the primer being used.

what grit sand paper should be used to rough up the surface for final paint?
through my sanding, ive noticed the truck has about 4 coats of paint on it. i was thinking of just sanding the truck down to the stock coat of paint, because ive heard it is fine to paint over the factory paint. should i just take all the paint off and prime the whole truck, or is the factory coat a good base?
does anyone have any recommendations for the brand of spray paint to use?
once the paint is laid down, what grit paper should be used in final wetsanding to get the surface ready for clearcoat?
is there a spray can of clearcoat which would give a decent finish?
if so, what grit paper should be used on the paint to prep for clearcoat?
what are the final steps that need to be done to get a nice finish on the clearcoat? (grit sandpaper for each step, and final buffing)
my father wants me to do all the prep work then turn the truck over to someone else such as maaco or a local body shop to lay down the paint. how much would this typically cost if ive done all of the prep work?

ive thought about doing the roll on paint idea, but it takes so long to dry and im doing this whole project outside, im afraid dust will get into the paint before it can dry. im leaning towards blue because gloss black shows too many imperfections and waves.

if anyone has any tips or tricks or ideas please feel free to post them, ive never attempted to do this before and want to get a decent paint job for cheap that can be done in the gravel parkinglot of my apartment.
thanks